As a technique to improve an output of an engine, a method (supercharging) of compressing intake air with a turbocharger and supplying an engine with the compressed intake air is known. A typical turbocharger includes an exhaust turbine driven to rotate by exhaust gas flowing through an exhaust channel of an engine, and a compressor turbine for sending intake air in an intake channel into a combustion chamber, the exhaust turbine and the compressor turbine being coupled to each other. The exhaust turbine is driven to rotate by energy of exhaust gas, and the compressor turbine is driven to rotate in accordance with the exhaust turbine. As a result, intake air in the intake channel is supercharged and sent into the combustion chamber, and thereby an output of the engine improves.
In the turbocharger, the exhaust turbine and a turbo bearing are exposed to oil component contained in lubricant oil or exhaust gas under a high-temperature environment, and thus deterioration is likely to occur by sticking or coking of the oil component. Progress of such deterioration leads to wear of components of the turbocharger to decrease fuel-consumption performance of the engine, and even results in malfunction. Thus, early detection of deterioration is desirable.
Patent Document 1 discloses a technique to detect deterioration of a turbocharger of such type. The technique to detect deterioration of a turbocharger disclosed in Patent Document 1 is for a turbocharger equipped with a waste-gate valve, and is to perform abnormality determination on the basis of whether a rotation-speed change that accompanies opening and closing of the waste-gate valve is in a predicted range.